A. N. (Thanos) Papanicolaou

Quantifying Sediment Sources to the Suspended Load of an Agricultural Stream Using Radioisotopes

The goal of this study was to understand better the delivery of sediment to streams in small, intensively agricultural watersheds of the U.S. Midwest by determining the amount of sediment coming from the fields and stream banks during three consecutive runoff events. The natural activities of Beryllium-7 and Lead-210 in different source soils were compared with the corresponding activities of the suspended sediment collected in the stream during these events. Both a simple two end-member mixing model and a Bayesian model were used to determine the relative contributions from the source areas to the suspended load of each event. The two end-member approach suggested that ~60% of the sediment carried in the stream during the first event was eroded upland soils and was attributed to a “first flush” of readily available material from past events. For the second and third events, the amounts of eroded upland soils were ~34% and ~26%, respectively, because less material was readily available for mobilization. The two end-member model results compared favorably with the Bayesian model, which also incorporated Cesium-137 as a third tracer. Additionally, these results were confirmed with the clockwise hysteresis observed in the different events. During the third event, a flash flood, stream bank collapse was observed and bank retreat estimates from multiple methods compared favorably with the partitioning results. Quantifying sediment sources in watersheds will allow land managers to target more accurately areas where Best Management Practices (BMPs) are most needed to control sediment-related problems. INTRODUCTION Quantifying erosion and sediment delivery at the watershed scale has proven difficult due to high temporal and spatial variability of the different erosion processes occurring over a landscape (Church 2006), despite recent progress in understanding the mechanisms of erosion (e.g., Romkens et al. 2002; Govers et al. 2007). This problem is further exacerbated in agricultural areas where anthropogenic activities, including tillage (e.g., Van Oost et al. 2006) and channel straightening (e.g., Urban and Rhoads 2003) are added stressors. The need still exists to identify and quantify 1243 World Environmental and Water Resources Congress 2014: Water without Borders

Calibration of a Geophone Acoustic Sensor to Bedload Particle Mode of Transport

Geophones are passive acoustic instruments, which can provide continuous, unattended bedload transport rate measurements, based on the acoustic energy generated by the impacts of transported bedload particles onto a metal plate mounted on the geophone. The purpose of the present study is to investigate the correspondence of the geophone acoustic signal recording frequency with the mode of bedload particle transport, i.e., rolling and saltation. Controlled experiments corresponding to near incipient, marginal, and general bedload motion were conducted. The geophone was configured to record impacts the lower “Frequency 1” (100-200 kHz) and the higher “Frequency 4” (380-480 kHz) bands. Rolling particles produced responses predominantly in the lower Frequency 1, but also weaker responses in the higher Frequency 4, which were attributed to the particle rotational vibrations. Instead, saltating particles generated responses mainly in Frequency 4 and only weaker responses in Frequency 1, due to particle spheroid vibrations. This study complements efforts for improving the accuracy of geophone calibration curves and hence in quantifying bedload rates under the rolling and saltating transport modes.

Examining seasonal trends in sediment source contributions in an intensely cultivated Midwestern sub-watershed using Bayesian un-mixing

This study aims to shed some light on the dynamics of sediment source contributions in the South Amana Sub-Watershed (SASW) in Iowa, USA, at a seasonal scale. Field studies were performed periodically from April to August 2007, in which sediment source and eroded samples were collected from the uplands and the stream network. The δ 13 C and δ 15 N signatures of the samples were obtained via mass spectrometry and used as “fingerprints” to identify the different contributing sources. For sources that were not sampled, literature values of δ 13 C and δ 15 N from similar systems in the region were adopted. Un-mixing of the eroded samples using the tracer signatures was achieved with an enhanced version of an existing Bayesian, Markov Chain Monte Carlo (MCMC) model, structured to well represent the intensely cultivated SASW system. Balance in sediment source contributions shifted between upland and in-streams sources over the season. Preliminary results from the study confirm observations from other studies that hydrological factors and sediment availability significantly affect the relative contributions of upland and in-stream sources. In addition, the study shows that canopy cover vs. bare soil plays an important role and should be taken into consideration when performing un-mixing studies designed to identify sediment sources.

Framework for Bridge Scour Measurement Using Radio Frequency IDentification (RFID)

Scour around bridge piers can undermine the bridge integrity and cause catastrophic bridge failures. The goal of this coupled experimental and theoretical study is to set a framework for applying Radio Frequency IDentification (RFID) technology to develop a bridge scour remote monitoring system. RFID involves the wireless exchange of information between a base station (reader) and a transponder via an antenna. The proposed bridge scour monitoring system utilizes the Return Signal Strength Indicator (RSSI) of a transponder buried in the vicinity of the pier to determine the transponder distance from the antenna and thus the scour depth. In this study we present a novel methodology for experimentally determining the RSSI voltage for a low frequency (134.2 kHz), passive RFID system.